1. Field of the Invention
The present invention relates to a technique of forming an adequate distribution of ink dots of respective colors on a printing medium, so as to print an image expressed in a wide range of natural colors.
2. Description of the Related Art
In a printing apparatus that ejects ink droplets of various color inks from a print head and thereby expresses an image of natural colors on a printing medium, four color inks, that is, cyan (C), magenta (M), yellow (Y), and black (K), are basically used to create ink dots and print an image. The printing apparatus regulates the hue and the lightness, which are indexes representing the color, so as to print an image expressed in a wide range of natural colors. The hue, that is, the xe2x80x98colorxe2x80x99 or xe2x80x98tintxe2x80x99, such as red or blue, is regulated by changing the ratio of dots of the C, M, and Y inks ejected from the print head. The lightness is, on the other hand, regulated by changing the density of dots. Regulating the ratio and the density of dots created with the respective color inks on the printing medium enables a printed image to have a wide range of natural colors.
Some recently developed printing apparatus use light cyan (LC) ink and light magenta (LM) ink, (additionally light yellow (LY) ink in some cases) in addition to the above four basic color inks, so as to significantly improve the picture quality in an area of high lightness. In the case where an image in the area of high lightness (that is, the highlighted area) is printed with only four color inks, C, M, Y, and K, a sparse distribution the C and M dots undesirably makes these dots conspicuous and thereby lowers the picture quality of the printed image. The phenomenon of making the dots conspicuous to worsen the picture quality is expressed by the term xe2x80x98poor granularityxe2x80x99. It is difficult to reproduce the image information with regard to a fine part with the sparsely distributed dots. This is also the reason of the poor picture quality of the resulting printed image with only the four color inks, C, M, Y, and K. The dots of the LC and LM inks (additionally LY ink in some occasions) are, on the other hand, not so conspicuous as the dots of the C and M dots and thereby do not lower the picture quality of the highlighted area. The LC and LM inks enable the dots to be formed at a higher density than the C and M inks. This accordingly enables reproduction of the image information with regard to the fine part and further improves the picture quality. Because of these reasons, the printing apparatus using the six color inks including the LC and LY inks (or the seven color inks further including the LY ink) improves the picture quality of the highlighted area.
The prior art printing apparatus including those using the light inks, however, can not sufficiently improve the picture quality in an area of low lightness (that is, the shadow area), because of the reasons discussed below. Especially the printing apparatus using the light inks have an insufficient improvement in picture quality in the shadow area, while significantly improving the picture quality in the highlighted area.
This problem is explained with an example of a gradation pattern from red to black with a gradual decrease in lightness. The color xe2x80x98redxe2x80x99 is reproduced by mixture of magenta dots and yellow dots. The lightness is lowered by addition of cyan dots or black dots. Formation of black dots on red dots makes the black dots extremely conspicuous in an area supposed to have a homogeneous color. This results in the poor granularity. The dots of cyan, which is complementary to red, are also rather conspicuous on the red dots, although the degree of conspicuousness is lower than that of the black dots. Formation of cyan dots on red dots thus also results in the rather poor granularity. As in the case of the highlighted area, the use of the light cyan ink effectively improves the granularity. From the viewpoint of the improvement in granularity, the light cyan ink is most preferable over the cyan ink and the black ink to form dots over the red dots. Addition of the cyan dots or the black dots on the red dots having a sufficiently low lightness, however, does not make the cyan dots or the black dots so conspicuous but keeps the granularity at a fair level.
There is a restriction of total quantity of ink ejected per unit area on the printing medium, and it is impossible to heighten the density of dot formation limitlessly. This restriction is referred to as the restriction of ink duty. Ejection of ink over the allowed density of dots causes blots or wrinkles on the printing medium. In order to avoid such problems, each printing medium has a preset maximum density of dots (restriction of ink duty). The total density of dots created with the respective inks should not exceed this restriction of ink duty.
When the gradation pattern from red to black is printed, it is required to add the light cyan dots or the cyan dots. The color xe2x80x98redxe2x80x99 is originally expressed by a large number of yellow dots and magenta dots as mentioned previously. Formation of even a small number of light cyan dots or cyan dots thus causes the total quantity of ink to reach the restriction of ink duty. In the course of the gradation, there is accordingly a prohibition of further addition of the light cyan dots or the cyan dots. In the practical operation, when there is some margin for the restriction of ink duty, light cyan dots are added to red dots to lower the lightness. When the total quantity of ink reaches the restriction of ink duty, even if the cyan dots may have adverse effects on the granularity of the resulting printed image, the cyan dots instead of the light cyan dots should be formed to further decrease the lightness. When the total quantity of ink again reaches the restriction of ink duty under the condition of the perfect replacement of the light cyan dots with the cyan dots, even if the black dots are conspicuous, the black dots instead of the cyan dots should be formed to further decrease the lightness. In the shadow area (the area of low lightness) having the gradation from red to black, the cyan dots and the black dots are often used irrespective of their conspicuousness, because of the restriction of ink duty. This naturally results in the poor granularity.
The above description regards the example of printing the gradation pattern from red to black. The formation pattern of ink dots should be specified under the various limitations including the improvement in granularity and the restriction of ink duty. The design of the optimum dot formation pattern accordingly requires a lot of time and labor with the trial and error.
The object of the present invention is thus to enhance the degree of freedom in specification of dot on-off conditions with regard to a plurality of different inks and thereby improve the picture quality in a specific area including a low lightness area (shadow area).
At least part of the above and the other related objects is actualized by a printing system, which includes a printer that creates dots with a plurality of different inks, so as to print an image on a printing medium, and a print controller that supplies control information to the printer, so as to control the creation of dots with the plurality of different inks. The print controller includes: a dot on-off condition specification unit that specifies dot on-off conditions with regard to a plurality of basic color inks and a dark ink based on input image data, the plurality of basic color inks being combined with one another to express achromatic color, the dark ink having a main wavelength region of light absorption substantially identical with that of one basic color ink selected out of the plurality of basic color inks but a lower lightness than that of the selected basic color ink; and a control information output unit that outputs the specification of the dot on-off conditions with regard to the plurality of basic color inks and the dark ink to the printer as the control information. The printer includes: a control information input unit that receives the specification of the dot on-off conditions with regard to the plurality of basic color inks and the dark ink, which is output from the control information output unit, as the control information; and a dot formation unit that creates dots with the plurality of basic color inks and the dark ink, based on the input control information.
The present invention is also directed to a method of printing, which corresponds to the printing system discussed above. The present invention accordingly provides a method of creating dots with a plurality of different inks, so as to print an image on a printing medium. The method includes the steps of: specifying dot on-off conditions with regard to a plurality of basic color inks and a dark ink based on input image data, the plurality of basic color inks being combined with one another to express achromatic color, the dark ink having a main wavelength region of light absorption substantially identical with that of one basic color ink selected out of the plurality of basic color inks but a lower lightness than that of the selected basic color ink; and creating dots with the plurality of basic color inks and the dark ink, based on the specification of the dot on-off conditions with regard to the plurality of basic color inks and the dark ink, so as to print an image.
In the printing system and the corresponding method of the present invention, the dot on-off conditions with regard to the plurality of basic color inks and the dark ink are specified, based on the input image data. Here the plurality of basic color inks are combined with one another to create ink dots and thereby express achromatic color. The dark ink includes one basic color ink selected out of the plurality of basic color inks as a primary component and another ink having a specific hue different from the hue of the selected basic color ink. The dark ink has a lower lightness than that of the selected basic color ink. The dark ink may alternatively have a different ink composition from that of the selected basic color ink but equivalent spectroscopic characteristics to those of the selected basic color ink. When the selected basic color ink is yellow ink, for example, the dark ink may be obtained by adding adequate quantities of cyan and magenta dyes to the yellow ink or by adding an adequate quantity of black dye to the yellow ink. The technique of the present invention creates dots with the plurality of basic color inks and the dark ink on the printing medium, based on the specification of dot on-off conditions with regard to the respective inks, so as to print an image. This arrangement enables dots to be created with the dark ink having the characteristics discussed above, as well as with the plurality of basic color inks. This enhances the degree of freedom in specification of dot on-off conditions and thereby improves the picture quality of a resulting printed image. Specifying the dot on-off conditions with regard to not only the basic color inks but the dark ink results in improving the picture quality, because of the functions discussed below.
As mentioned above, the dark ink includes one basic color ink selected out of the plurality of basic color inks as a primary component and another ink having a specific hue different from the hue of the selected basic color ink, and has a lower lightness than that of the selected basic color ink. A certain color conventionally expressed by a combination of the plurality of basic color inks may be expressible by only the dark ink or by a combination of the dark ink with small quantities of one or plural basic color inks. In such cases, expression of the certain color by the combination of the dark ink with one or plural basic color inks requires a less total quantity of inks, compared with the expression of the certain color by the combination of the plurality of basic color inks. The use of the dark ink thus improves the picture quality, which is worsened by the restriction of ink duty. For example, the use of the dark ink desirably keeps the fair granularity in a shadow area, where the granularity is readily worsened by the restriction of ink duty.
A print controller of the present invention is applicable to such a printing system. The present invention is accordingly directed to a print controller that supplies control information to a printer, which creates dots with a plurality of different inks, in order to control the creation of dots with the plurality of different inks. The printer creates dots with a plurality of basic color inks as well as with a dark ink, wherein the plurality of basic color inks are combined with one another to express achromatic color, and the dark ink has a main wavelength region of light absorption substantially identical with that of one basic color ink selected out of the plurality of basic color inks but a lower lightness than that of the selected basic color ink. The print controller includes: a dot on-off condition specification unit that specifies dot on-off conditions with regard to the plurality of basic color inks and the dark ink, based on input image data; and a control information output unit that outputs the specification of the dot on-off conditions with regard to the plurality of basic color inks and the dark ink to the printer as the control information.
The present invention is further directed to a method of controlling a printing operation, which corresponds to the print controller discussed above. The present invention accordingly provides a method of supplying control information to a printer, which creates dots with a plurality of different inks on a printing medium, in order to control the creation of dots with the plurality of different inks and thereby controlling a printing operation of the printer. The method includes the steps of: (a) specifying dot on-off conditions with regard to a plurality of basic color inks and a dark ink based on input image data, the plurality of basic color inks being combined with one another to express achromatic color, the dark ink having a main wavelength region of light absorption substantially identical with that of one basic color ink selected out of the plurality of basic color inks but a lower lightness than that of the selected basic color ink; and (b) outputting the specification of the dot on-off conditions with regard to the plurality of basic color inks and the dark ink to the printer as the control information, so as to control the printing operation of the printer.
In the print controller and the corresponding method of controlling the printing operation, the dot on-off conditions with regard to the plurality of basic color inks and the dark ink are specified, based on the input image data. The specification of the dot on-off conditions is supplied to the printer as the control information to control creation of dots with the plurality of basic color inks and the dark ink.
The technique of the present invention provides the plurality of basic color inks and the dark ink in the printer, which creates dots with a plurality of different inks on a printing medium, and supplies the control information to the printer. This arrangement enables creation of ink dots with the plurality of different inks including the dark ink, thus printing an image of high picture quality.
In accordance with one preferable application of the print controller and the corresponding method of controlling the printing operation, a color conversion table is provided to store mappings of tints used to express a color image to combinations of the plurality of basic color inks and the dark ink to represent the tints. In this application, the dot on-off conditions with regard to the plurality of basic color inks and the dark ink are specified by referring to the color conversion table.
The method of referring to the color conversion table enables the dot on-off conditions of the respective inks to be specified quickly and accurately.
In accordance with another preferable application of the print controller, the dot on-off conditions with regard to the plurality of basic color inks and the dark ink are specified, based on a preset proportion regarding dots of the plurality of basic color inks and dots of the dark ink.
When the dot on-off conditions are specified with regard to the dark ink as well as the plurality of basic color inks, the proportion of the dots with the respective inks may take a variety of values. The arrangement of specifying the dot on-off conditions based on the proportion set equal to an appropriate value enables an image of high picture quality to be printed.
In accordance with still another preferable application of the print controller, the dark ink has lower lightness and saturation than those of one basic color ink selected out of the plurality of basic color inks. The dark ink is obtained, for example, by adding the dye of another ink to the selected basic color ink.
The use of the dark ink enhances the degree of freedom in specification of the dot on-off conditions and thereby improves the picture quality of the resulting printed image. The use of the dark ink, which is obtained by adding at least one dye of another ink to lower the lightness and the saturation, may enable a specific color conventionally expressed by a combination of the plurality of basic color inks to be expressed by only the dark ink or by a combination of the dark ink with small quantities of one or plural basic color inks. The expression of the specific color by the combination of the dark ink with the basic color inks reduces the total quantity of inks and thus improves the picture quality, which is worsened by the restriction of ink duty.
The dark ink may alternatively have a main wavelength region for most strongly absorbing a ray in a visible range, which is substantially identical with that of one basic color ink selected out of the plurality of basic color inks, and a greater integral of light absorptivity in a wavelength region of the visible range than that of the selected basic color ink.
The use of the dark ink enhances the degree of freedom in specification of the dot on-off conditions and thereby improves the picture quality of the resulting printed image.
The main wavelength region for most strongly absorbing a ray in a visible range is approximately equal to a range of 600 nm to 700 nm to absorb a red ray in the case of cyan ink, equal to a range of 500 nm to 600 nm to absorb a green ray in the case of magenta ink, and equal to a range of 400 nm to 500 nm to absorb a blue ray in the case of yellow ink. Since the absorptivity of light gently varies, the half-width (that is, the wavelength region having the absorptivity that is half the maximum absorptivity) may be adopted in the case where there is a difficulty in identifying the wavelength region.
The dark ink may have the main wavelength region, which is mostly included in a wavelength region of 400 nm to 500 nm, and a smaller light absorptivity in the vicinity of 700 nm than a mean light absorptivity in a wavelength region of 600 nm to 700 nm.
It is known that the sensitivity of the vision of human eye to the color gradually lowers in a wavelength range of about 650 nm and is significantly low in the vicinity of 700 nm. Irrespective of a large variation in spectroscopic characteristics of the ink in the vicinity of the wavelength of 700 nm, there is no significantly difference in hue recognized by the vision of the human eye. Namely the spectroscopic characteristics of the ink have a large degree of freedom in the vicinity of the wavelength of 700 nm. The ink having a favorable hue is thus prepared by utilizing this large degree of freedom. The dark ink having the favorable hue has the smaller light absorptivity in the vicinity of 700 nm than the mean light absorptivity in the wavelength region of 600 nm to 700 nm. The main wavelength region that is mostly included in the wavelength region of 400 nm to 500 nm is substantially opposite to the range in the vicinity of 700 nm having the large degree of freedom across the visible range. This facilitate the design of the ink.
The dark ink may have the main wavelength region, which is mostly included in a wavelength region of 400 nm to 500 nm, and a greater light absorptivity in the vicinity of 700 nm than a mean light absorptivity in a wavelength region of 600 nm to 700 nm. The greater light absorptivity in the vicinity of 700 nm than the mean light absorptivity in the wavelength region of 600 nm to 700 nm enables the dark ink to have a more preferable hue, because of the reason discussed above.
The dark ink, whose dot on-off conditions are specified by the print controller of the present invention may have:
(A) a characteristic wavelength region for strongly absorbing a ray in a visible range to mainly determine the hue of the dark ink, which is substantially identical with a characteristic wavelength region of one basic color ink selected out of the plurality of basic color inks;
(B) a mean value of light absorptivity that is greater than or substantially identical with a mean value of light absorptivity of the selected basic color ink in the characteristic wavelength region of the dark ink; and
(C) a mean value of light absorptivity that is greater than a mean value of light absorptivity of the selected basic color ink in a wavelength region of visible light except the characteristic wavelength region of the dark ink.
The dark ink satisfying the above condition (A) has a hue close to the hue of the corresponding basic color ink, so that a specific color conventionally expressed by a combination of the plurality of basic color inks is, in many cases, expressible by a combination of the dark ink with one or plural basic color inks. Expression of the specific color by the combination of the dark ink satisfying the above conditions (B) and (C) with one or plural basic color inks requires the less total quantity of inks than expression of the specific color by the combination of the plurality of basic color inks. The use of the dark ink satisfying all the above conditions (A) through (C) thus reduces the total quantity of ink consumption in many cases. This arrangement effectively prevents the poor granularity and improves the picture quality, which is worsened by the restriction of ink duty as discussed previously.
The dark ink may have the characteristic wavelength region, which is mostly included in a wavelength region of 400 nm to 500 nm, and a smaller light absorptivity in the vicinity of 700 nm than a mean light absorptivity in a wavelength region of 600 nm to 700 nm.
As described above, even when the light absorptivity in the vicinity of 700 nm varies, the hue of the ink recognizable by the vision of the human eye does not have any significant variation. It is accordingly expected that the spectroscopic characteristics of the ink have a large degree of freedom in the vicinity of the wavelength of 700 nm. The smaller light absorptivity in the vicinity of 700 nm than the mean light absorptivity in the wavelength region of 600 nm to 700 nm enables the dark ink to have a more favorable hue. Setting the characteristic wavelength region of the dark ink to be substantially opposite to the range in the vicinity of 700 nm having the large degree of freedom across the visible range facilitates the design of the ink.
The dark ink may have the characteristic wavelength region, which is mostly included in a wavelength region of 400 nm to 500 nm, and a greater light absorptivity in the vicinity of 700 nm than a mean light absorptivity in a wavelength region of 600 nm to 700 nm.
As described previously, there is a large degree of freedom in setting the light absorptivity in the vicinity of the wavelength of 700 nm. The greater light absorptivity in the vicinity of 700 nm than the mean light absorptivity in the wavelength region of 600 nm to 700 nm may enable the dark ink to have a more favorable hue.
The dark ink, whose dot on-off conditions are specified by the print controller of the present invention, may have a hue in a specific hue range interposed between a red hue zone and a green hue zone on a Munsell hue circle, and have a lower lightness than that of a basic color ink out of the plurality of basic color inks, which has a hue in the specific hue range.
The specific hue range interposed between the red hue zone and the green hue zone on the Munsell hue circle roughly corresponds to the hue of yellow. The color of yellow has a relatively high lightness. Dots of the dark yellow ink having the lower lightness than that of the yellow ink are still not conspicuous. Creating dots with such a dark ink thus significantly improves the picture quality of the resulting printed image.
The dark ink may have a hue in the specific hue range that includes a yellow hue zone and extends to a boundary between the yellow hue zone and the green hue zone on the Munsell hue circle. The ink in this specific hue range has the hue of greenish yellow. Creating dots with such a dark ink significantly improves the picture quality of the resulting printed image having the little greenish hue.
The dark ink may have a hue in the specific hue range that includes a yellow hue zone and extends to a boundary between the yellow hue zone and the red hue zone on the Munsell hue circle, and a smaller saturation than that of flesh color. The ink in the specific hue range that includes the yellow hue zone and extends to the boundary between the yellow hue zone and the red hue zone on the Munsell hue circle has the hue of reddish yellow. Creating dots with such a dark ink significantly improves the picture quality of the resulting printed image having the little reddish hue. The color that is included in the specific hue range and has a relatively large saturation is close to the xe2x80x98flesh colorxe2x80x99. When the ink having the hue of reddish yellow is used as the dark ink, it is preferable that the ink has a smaller saturation than that of flesh color. The dark ink of smaller saturation significantly improves the picture quality of the resulting printed image. It is accordingly preferable that the dark ink has a hue in the specific hue range that includes the yellow hue zone and extends to the boundary between the yellow hue zone and the red hue zone on the Munsell hue circle, and a smaller saturation than that of flesh color.
The dark ink may have a hue included in a specific range of 10R to 10GY on a Munsell hue circle, and a lower lightness than that of a basic color ink out of the plurality of basic color inks, which has a hue in the specific range.
The ink in the specific range roughly has the hue of yellow. Creating dots with such a dark ink significantly improves the picture quality of the resulting printed image.
The dark ink may have a saturation of smaller than 3.5C on a Munsell chroma when the hue of the dark ink is in a range of 2.5YR to 7.5YR on the Munsell hue circle.
The ink having the hue in the range of 2.5YR to 7.5YR on the Munsell hue circle and the saturation of greater than 3.5C on the Munsell chroma has the tint close to the flesh color. When an image having the greenish hue is printed, the use of the dark ink having a smaller saturation than that of xe2x80x98flesh colorxe2x80x99 has better effects on improvement of the picture quality. It is accordingly preferable that the dark ink has a saturation of smaller than 3.5C on the Munsell chroma when the hue of the dark ink is in the range of 2.5YR to 7.5YR on the Munsell hue circle.
The hue of the dark ink may be in a range of 10YR to 10GY on the Munsell hue circle. The ink in this range has the hue of greenish yellow. Creating dots with such a dark ink significantly improves the picture quality of the resulting printed image having the little greenish hue.
The dark ink may have the hue in a range of 10Y to 10R on the Munsell hue circle and a saturation of smaller than 3.5C on a Munsell chroma. The ink having the hue in the range of 10Y to 10R on the Munsell hue circle and the saturation of greater than 3.5C on the Munsell chroma has the tint close to the flesh color. When an image having the reddish hue is printed, the use of the dark ink having a smaller saturation than that of xe2x80x98flesh colorxe2x80x99 has better effects on improvement of the picture quality. It is accordingly preferable that the dark ink has the hue in a range of 10Y to 10R on the Munsell hue circle and a saturation of smaller than 3.5C on the Munsell chroma.
In accordance with one preferable application of the print controller that specifies the dot on-off conditions of the respective inks based on the image data, the technique specifies the dot on-off conditions with regard to the plurality of basic color inks and the dark ink, as well as with regard to at least one light ink, which has a hue substantially identical with that of at least one basic color ink selected out of the plurality of basic color inks but a lower density than that of the at least one basic color ink. The results of the specification are output to the printer as the control information to control the creation of dots with the plurality of different inks. The printer creates dots with the plurality of basic color inks, the dark ink, and the at least one light ink on a printing medium, according to the control information.
As described previously, the printing apparatus using the light ink remarkably improves the picture quality in the highlighted area but has less effects on improvement of the picture quality in the shadow area, because of the restriction of ink duty. Additionally using the dark ink improves the picture quality in the shadow area and thus attains the improvement in picture quality in the whole image.
In accordance with one preferable application of the print controller that specifies the dot on-off conditions of the respective inks based on the image data, the technique outputs the control information to control the creation of dots to a printer that creates at least two variable-size dots having different sizes with the respective inks. The technique specifies the dot on-off conditions as well as the sizes of the dots to be formed by the printer with regard to the plurality of different inks and supplies the results of the specification to the printer. The printer creates the adequate size dots with the plurality of different inks, based on the control information.
Varying the size of the ink dot by the printer that enables creation of at least two variable-size dots having different sizes significantly improves the picture quality of the resulting printed image. In this application, using the dark ink enhances the degree of freedom in specification of the dot on-off conditions and improves the picture quality, which is worsened by the restriction of ink duty.
In accordance with one preferable application of the print controller that specifies the dot on-off conditions of the respective inks based on the image data and the corresponding method of controlling the printing operation, the technique specifies the dot on-off conditions with regard to the plurality of basic color inks, which include at least yellow ink, as well as with the dark yellow ink, which has a main wavelength region of light absorption substantially identical with that of the yellow ink but a lower lightness than that of the yellow ink. The results of the specification are output to a printer that enables creation of dots with the plurality of basic color inks and the dark yellow ink. The printer receives the specification of the dot on-off conditions and creates dots with the plurality of basic color inks including at least the yellow ink and with the dark yellow ink, so as to print an image.
The yellow ink has a relatively high lightness. Even the dark yellow ink, which is darker than the yellow ink, still has a high lightness, so that dots of the dark yellow ink are relatively inconspicuous. Creation of dots with the dark yellow ink thus significantly improves the picture quality of the resulting printed image.
In accordance with one preferable application of the print controller of the present invention, the dot on-off conditions are specified with regard to at least the cyan ink, the magenta ink, and the yellow ink as the plurality of basic color inks. In this case, the dark ink may have a hue that is closest to the hue of the yellow ink among the cyan ink, the magenta ink, and the yellow ink. Specification of the dot on-off conditions with regard to the dark ink is carried out to enable dots with the dark ink to be created together with dots of at least one of the basic color inks when an image to be printed has hues varying from red to green on a Munsell hue circle.
The image having hues varying from red to green on the Munsell hue circle is printed by adequately creating dots of the magenta ink or dots of the cyan ink together with the dots of the yellow ink. The technique of this application enables the image having such hues to be alternatively printed by adequately creating dots of the dark ink together with the dots of the basic color ink. This arrangement effectively enhances the degree of freedom in specification of the dot on-off conditions with regard to each color ink, thereby improving the picture quality of the resulting printed image.
In accordance with one preferable application of the print controller of the present invention, the dot on-off conditions are specified with regard to at least the cyan ink, the magenta ink, and the yellow ink as the plurality of basic color inks. In this case, the dark ink may have a hue that is closest to the hue of the yellow ink among the cyan ink, the magenta ink, and the yellow ink. Specification of the dot on-off conditions with regard to the dark ink is carried out to enable dots with the dark ink to be created prior to creation of dots with either one of the cyan ink and the magenta ink when an image to be printed has hues varying from yellow to black.
Dots of the magenta ink or the cyan ink are rather conspicuous in an yellow image, unless the yellow image has a sufficiently low lightness. When an image to be printed has hues varying from yellow to black, creation of dots with the dark ink prior to creation of dots with the magenta ink or the cyan ink lowers the lightness of the image and makes the dots of the magenta ink or the cyan ink sufficiently inconspicuous. The hue of the dark ink is closest to the hue of the yellow ink. Creation of dots with the dark ink in the yellow image prior to creation of dots with the magenta ink or the cyan ink accordingly does not make the dots of the dark ink conspicuous to lower the picture quality. Using the dark ink having the above characteristics thus preferably improves the picture quality of the resulting printed image. The dots of the light cyan ink, which has the lower density than that of the cyan ink, and the dots of the light magenta ink, which has the lower density than that of the magenta ink, are not so conspicuous in an image having a relatively high lightness. Dots of the dark ink may thus be created in an overlapping manner on the dots of the light cyan ink or on the dots of the light magenta ink. In the case of a variable-dot printer, small-size dots are not so conspicuous even when they are created in an image having a relatively high lightness. Like in the case of the light ink, dots of the dark ink may thus be created in an overlapping manner on the small-size dots of the cyan ink or on the small-size dots of the magenta ink.
In accordance with one preferable application of the print controller of the present invention, the dot on-off conditions are specified with regard to at least the cyan ink, the magenta ink, and the yellow ink as the plurality of basic color inks. In this case, the dark ink may have a hue that is closest to the hue of the yellow ink among the cyan ink, the magenta ink, and the yellow ink, and a lower lightness than that of the yellow ink. Specification of the dot on-off conditions with regard to the dark ink is carried out to enable dots with the dark ink to be created prior to creation of dots with either one of the cyan ink and the magenta ink when an image to be printed has hues varying from color of the either one of the cyan ink and the magenta ink to black.
Dots of the cyan ink in a magenta image or dots of the magenta ink in a cyan image are rather conspicuous, unless the image has a sufficiently low lightness. When an image to be printed has hues varying from magenta to black or hues varying from cyan to black, creation of dots with the dark ink prior to creation of dots with the magenta ink or the cyan ink desirably lowers the lightness of the image and makes the dots of the magenta ink or the cyan ink sufficiently inconspicuous. The dark ink has the hue closest to the hue of the yellow ink. Like the dots of the yellow ink, dots of the dark ink are thus relatively inconspicuous in both the magenta image and the cyan image. Creation of dots with the dark ink prior to creation of dots with the magenta ink or the cyan ink accordingly does not make the dots of the dark ink conspicuous to lower the picture quality. Using the dark ink having the above characteristics thus preferably improves the picture quality of the resulting printed image. The dots of the light cyan ink and the dots of the light magenta ink are not so conspicuous in an image having a relatively high lightness. Dots of the dark ink may thus be created in an overlapping manner on the dots of the light cyan ink or on the dots of the light magenta ink. In the case of a variable-dot printer, small-size dots are not so conspicuous even when they are created in an image having a relatively high lightness. Like in the case of the light ink, dots of the dark ink may thus be created in an overlapping manner on the small-size dots of the cyan ink or on the small-size dots of the magenta ink.
In accordance with one preferable application of the print controller of the present invention, the dot on-off conditions are specified with regard to at least the cyan ink, the magenta ink, and the yellow ink as the plurality of basic color inks. In this case, the dark ink may have a hue that is closest to the hue of the yellow ink among the cyan ink, the magenta ink, and the yellow ink, and a lower lightness than that of the yellow ink. Specification of the dot on-off conditions with regard to the dark ink is carried out to enable dots with the dark ink to be created after creation of dots with the yellow ink when an image to be printed has hues varying from color of either one of the cyan ink and the magenta ink to black.
Dots of the cyan ink in a magenta image or dots of the magenta ink in a cyan image are rather conspicuous, unless the image has a sufficiently low lightness. Creating yellow dots in such images lowers the lightness of the image to some extent. The dots of the cyan ink or the magenta ink may, however, be still rather conspicuous in these images. This technique creates dots with the dark ink subsequent to creation of dots with the yellow ink. This further lowers the lightness of the image and makes the dots of the magenta ink or the cyan ink sufficiently inconspicuous. The dark ink has the hue closest to the hue of the yellow ink. Like the dots of the yellow ink, dots of the dark ink are thus relatively inconspicuous in both the magenta image and the cyan image. Using the dark ink having the above characteristics thus preferably improves the picture quality of the resulting printed image.
In accordance with another preferable application of the print controller of the present invention, the dot on-off conditions are specified with regard to the plurality of basic color inks including at least the cyan ink, the magenta ink, and the yellow ink, as well as with regard to the light ink, which has a hue substantially identical with the hue of the cyan ink or the magenta ink but a lower density than that of the cyan ink or the magenta ink. In this case, the dark ink may have a hue that is closest to the hue of the yellow ink among the cyan ink, the magenta ink, and the yellow ink. Specification of the dot on-off conditions with regard to the dark ink is carried out to enable dots with the dark ink to be created after creation of dots with the light ink when an image to be printed has hues varying from yellow to black.
Dots of the magenta ink or the cyan ink are rather conspicuous in an yellow image, unless the yellow image has a sufficiently low lightness. When an image to be printed has hues varying from yellow to black, formation of dots with the light ink desirably lowers the lightness of the image. Formation of dots with the dark ink in addition to with the light ink further lowers the lightness of the image and thereby makes the dots of the magenta ink and the cyan ink more inconspicuous. The hue of the dark ink is closest to the hue of the yellow ink. The dots of the dark ink are thus inconspicuous in the yellow image and do not lower the picture quality. Using the dark ink having the above characteristics thus preferably improves the picture quality of the resulting printed image.
The light ink, whose dot on-off conditions are specified by the print controller, may be light cyan ink having a hue substantially identical with that of the cyan ink but a lower density than that of the cyan ink or light magenta ink having a hue substantially identical with that of the magenta ink but a lower density than that of the magenta ink. Dots of the dark ink may be created after creation of dots with these light inks. More specifically dots of the dark ink may be created after creation of dots with both the light cyan ink and the light magenta ink.
Creating dots with these light inks lowers the lightness in an yellow image. Creating dots with the dark ink further lowers the lightness in the yellow image. This makes the dots of the cyan ink and the magenta ink more inconspicuous and improves the picture quality of the resulting printed image.
In accordance with one preferable application of the print controller that specifies the dot on-off conditions of the respective inks based on the image data and the corresponding method of controlling the printing operation, the technique specifies dot on-off conditions with regard to a plurality of basic color inks, which include at least cyan ink, magenta ink, and yellow ink, as well as with dark yellow ink, which has a main wavelength region of light absorption substantially identical with that of the yellow ink but a lower lightness than that of the yellow ink. The results of the specification are output to a printer that enables creation of dots with the plurality of basic color inks and the dark yellow ink. The printer receives the specification of the dot on-off conditions and creates dots with the plurality of basic color inks including at least the cyan ink, the magenta ink, and the yellow ink and with the dark yellow ink, so as to print an image.
The yellow ink has a relatively high lightness. Even the dark yellow ink, which is darker than the yellow ink, still has a higher lightness than those of the cyan ink and the magenta ink. Dots of the dark yellow ink are accordingly not so conspicuous as dots of the cyan ink or the magenta ink. Using the dark yellow ink in addition to the cyan ink, magenta ink, and the yellow ink to create dots and print an image thus significantly improves the picture quality of the resulting printed image.
The printing apparatus of the present invention applicable to the printing system discussed above may have another arrangement. The present invention is accordingly directed to a printing apparatus that has a print head to create dots with a plurality of different inks on a printing medium, receives control information to control the creation of dots with the plurality of different inks, and actually creates dots with the plurality of different inks, based on the input control information, so as to print an image. The printing apparatus includes: a basic color ink supply unit that supplies a plurality of basic color inks to the print head, the plurality of basic color inks being combined with one another to express achromatic color; a dark ink supply unit that supplies a dark ink to the print head, the dark ink having a main wavelength region of light absorption substantially identical with that of one basic color ink selected out of the plurality of basic color inks but a lower lightness than that of the selected basic color ink; a control information input unit that receives the control information with regard to dots of the plurality of basic color inks and the dark ink; and a dot formation unit that drives the print head based on the input control information, so as to create dots with the plurality of basic color inks and the dark ink.
The present invention is also directed to a method of printing, which corresponds to the printing apparatus of the above configuration. The present invention thus provides a method of receiving control information to control creation of dots with a plurality of different inks and driving a print head, which creates dots with the plurality of different inks on a printing medium, based on the control information, so as to print an image. The method includes the steps of: (a) supplying a plurality of basic color inks and a dark ink to the print head, the plurality of basic color inks being combined with one another to express achromatic color, the dark ink having a main wavelength region of light absorption substantially identical with that of one basic color ink selected out of the plurality of basic color inks but a lower lightness than that of the selected basic color ink; (b) receiving the control information with regard to dots of the plurality of basic color inks and the dark ink; and (c) driving the print head based on the input control information to create dots with the plurality of basic color inks and the dark ink, thereby printing an image.
In the printing apparatus of the present invention and the corresponding method of printing, the print head is driven according to the input control information for controlling creation of dots with regard to the plurality of basic color inks and the dark ink. Dots with the plurality of basic color inks and the dark ink are then created on the printing medium to print an image.
The use of the dark ink in addition to the plurality of basic color inks enhances the degree of freedom in specification of dot on-off conditions and thus enables the adequate specification of the dot on-off conditions. The supplies of the plurality of basic color inks and the dark ink are fed to the print head, and the print head is then driven according to the results of the specification of the dot on-off conditions. This arrangement enables the dots to be adequately formed with the respective inks on a printing medium, so as to print an image of high picture quality.
In accordance with one preferable application of the present invention, the printing apparatus creates dots with at least cyan ink, magenta ink, and yellow ink as the dots with the plurality of basic color inks.
The creation of dots with at least the cyan ink, the magenta ink, and the yellow ink enables expression of a practically sufficient number of hues. The use of the dark ink in addition to these various color inks enhances the degree of freedom in specification of dot on-off conditions and thereby improves the picture quality of the resulting printed image.
In accordance with another preferable application of the present invention, the printing apparatus creates dots with at least black ink in addition to the cyan ink, the magenta ink, and the yellow ink. The printing apparatus also creates dots with dark yellow ink, which has a main wavelength region of light absorption substantially identical with that of the yellow ink but a lower lightness than that of the yellow ink.
Creation of dots with the black ink in addition to the cyan ink, the magenta ink, and the yellow ink further improves the picture quality of the resulting printed image. The use of the dark yellow ink in addition to these inks enhances the degree of freedom in specification of the dot on-off conditions and thereby improves the picture quality of the resulting printed image.
In accordance with another preferable application of the present invention, the printing apparatus creates dots with at least cyan ink, magenta ink, and yellow ink as the plurality of basic color inks, as well as with the dark ink and at least one light ink, which has a hue substantially identical with that of at least one basic color ink selected out of the plurality of basic color inks but a lower density than that of the at least one basic color ink.
Creation of dots with the variety of color inks including the light ink improves the picture quality of the resulting printed image. The use of the dark ink in addition to these various color inks enhances the degree of freedom in specification of the dot on-off conditions and thereby further improves the picture quality of the resulting printed image.
In accordance with sill another preferable application of the present invention, the printing apparatus creates at least two variable-size dots having different sizes with regard to at least cyan ink, magenta ink, and yellow ink as the plurality of basic color inks.
Creation of the at least two variable-size dots with regard to the respective inks improves the picture quality of the resulting printed image. The use of the dark ink in addition to these inks enhances the degree of freedom in specification of the dot on-off conditions and thereby further improves the picture quality of the resulting printed image.
In accordance with another preferable application of the present invention, the printing apparatus has an ink reservoir unit, in which the plurality of basic color inks and the dark ink are kept independently.
In the printing apparatus having the ink reservoir unit for independently keeping the plurality of basic color inks and the dark ink, supplies of the respective inks from the ink reservoir unit to the print head cause dots of the plurality of basic color inks and dots of the dark ink to be created on the printing medium. This results in printing an image of high picture quality. The arrangement of keeping the respective inks independently means that the respective inks should be accommodated in a non-miscible manner. These inks may be kept together in one ink reservoir unit or may be kept separately in different ink reservoir unit.
In this printing apparatus, the ink reservoir unit may keep a greater quantity of the dark ink than a quantity of the one basic color ink corresponding to the dark ink.
When natural images, such as landscapes and portraits, are printed, a greater quantity of the dark ink is generally consumed than the quantity of the basic color ink having the closest hue to that of the dark ink. The ink reservoir unit keeping the greater quantity of the dark ink than the quantity of the corresponding basic color ink thus favorably causes the quantities of the respective inks kept in the ink reservoir unit to be close to the actual quantities of ink consumption.
In accordance with one preferable application of the printing apparatus of the present invention and the corresponding method of printing, the print head is driven according to the input control information to create dots with the respective inks, wherein the control information controls creation of dots with the plurality of basic color inks, which include at least cyan ink, magenta ink, and yellow ink, as well as with dark yellow ink, which has a main wavelength region of light absorption substantially identical with that of the yellow ink but a lower lightness than that of the yellow ink.
In the printing apparatus of this arrangement and the corresponding method of printing, dots are created with the dark yellow ink as well as with the cyan ink, the magenta ink, and the yellow ink. This arrangement enhances the degree of freedom in specification of dot on-off conditions and thereby improves the picture quality of the resulting printed image.
In accordance with one preferable application of the present invention, the printing apparatus has an ink reservoir unit that keeps at least the cyan ink, the magenta ink, the yellow ink, and the dark yellow ink independently. The ink reservoir unit keeps a greater quantity of the dark yellow ink than a quantity of the yellow ink.
When natural images, such as landscapes and portraits, are printed, a greater quantity of the dark yellow ink is generally consumed than the quantity of the yellow ink. The ink reservoir unit keeping the greater quantity of the dark yellow ink than the quantity of the yellow ink thus favorably causes the quantities of the respective inks kept in the ink reservoir unit to be close to the actual quantities of ink consumption.
The technique of the present invention may be implemented by a computer, which reads a specific program that actualizes the functions of the printing system, the print controller, or the printing apparatus of the present invention discussed above. One application of the present invention is a recording medium, in which a specific program for attaining the functions of the printing system of the present invention is recorded. The present invention is thus directed to a recording medium, in which a specific program is recorded in a computer readable manner. The specific program actualizes a method of creating dots with a plurality of different inks, so as to print an image on a printing medium. The specific program causes a computer to attain the functions of: specifying dot on-off conditions with regard to a plurality of basic color inks and a dark ink based on input image data, the plurality of basic color inks being combined with one another to express achromatic color, the dark ink having a main wavelength region of light absorption substantially identical with that of one basic color ink selected out of the plurality of basic color inks but a lower lightness than that of the selected basic color ink; and controlling creation of dots with the plurality of basic color inks and the dark ink, based on the specification of the dot-on-off conditions with regard to the plurality of basic color inks and the dark ink.
Another application of the present invention is a recording medium, in which a specific program for attaining the functions of the print controller of the present invention is recorded. The present invention is thus directed to another recording medium, in which a specific program is recorded in a computer readable manner. The specific program actualizes a method of supplying control information to a printer, which creates dots with a plurality of different inks on a printing medium, in order to control the creation of dots with the plurality of different inks and thereby controlling a printing operation of the printer. The specific program causes a computer to attain the functions of: specifying dot on-off conditions with regard to a plurality of basic color inks and a dark ink based on input image data, the plurality of basic color inks being combined with one another to express achromatic color, the dark ink having a main wavelength region of light absorption substantially identical with that of one basic color ink selected out of the plurality of basic color inks but a lower lightness than that of the selected basic color ink; and outputting the specification of the dot on-off conditions with regard to the plurality of basic color inks and the dark ink to the printer as the control information, so as to control the printing operation of the printer.
Still another application of the present invention is a recording medium, in which a specific program for attaining the functions of the printing apparatus of the present invention is recorded. The present invention is thus directed to a recording medium, in which a specific program is recorded in a computer readable manner. The specific program actualizes a method of receiving control information to control creation of dots with a plurality of different inks and driving a print head, which creates dots with the plurality of different inks on a printing medium, based on the control information, so as to print an image. The specific program causes a computer to attain the functions of: receiving the control information to control creation of dots with a plurality of basic color inks and a dark ink, the plurality of basic color inks being combined with one another to express achromatic color, the dark ink having a main wavelength region of light absorption substantially identical with that of one basic color ink selected out of the plurality of basic color inks but a lower lightness than that of the selected basic color ink; and driving the print head based on the input control information to create dots with the plurality of basic color inks and the dark ink, thereby printing an image.
The computer reads any one of the specific programs recorded in the recording media to actualize the respective functions. Creation of dots with the dark ink as well as with the plurality of basic color inks improves the picture quality of the resulting printed image.
In accordance with one preferable application of the present invention, the specific program recorded in the recording medium for attaining the functions of the print controller further causes the computer to attain the function of storing in advance mappings of tints used to express a color image to combinations of the plurality of basic color inks and the dark ink to represent the tints. In this structure, the dot on-off conditions with regard to the plurality of basic color inks and the dark ink are specified, based on the mappings stored in advance. This arrangement ensures the quick and accurate specification of the dot on-off conditions.
The plurality of basic color inks generally include the cyan ink, the magenta ink, and the yellow ink. It is preferable that the dark ink has a hue close to the hue of the yellow ink, which has the highest lightness among these basic color inks. There is accordingly another possible application of the recording medium, in which a specific program for attaining the functions of the print controller is recorded. The present invention is thus directed to a recording medium, in which a specific program is recorded in a computer readable manner. The specific program actualizes a method of supplying control information to a printer, which creates dots with a plurality of different inks on a printing medium, in order to control the creation of dots with the plurality of different inks and thereby controlling a printing operation of the printer. The specific program causes a computer to attain the functions of: specifying dot on-off conditions with regard to a plurality of basic color inks and dark yellow ink based on input image data, the plurality of basic color inks including at least cyan ink, magenta ink, and yellow ink, the dark yellow ink having a main wavelength region of light absorption substantially identical with that of the yellow ink but a lower lightness than that of the yellow ink; and outputting the specification of the dot on-off conditions with regard to the plurality of basic color inks and the dark yellow ink to the printer as the control information, so as to control the printing operation of the printer.
There is also another possible application of the recording medium, in which a specific program for attaining the functions of the printing apparatus is recorded. The present invention is thus directed to a recording medium, in which a specific program is recorded in a computer readable manner. The specific program actualizes a method of receiving control information to control creation of dots with a plurality of different inks and driving a print head, which creates dots with the plurality of different inks on a printing medium, based on the control information, so as to print an image. The specific program causes a computer to attain the functions of: receiving the control information to control creation of dots with a plurality of basic color inks and dark yellow ink, the plurality of basic color inks including at least cyan ink, magenta ink, and yellow ink, the dark yellow ink having a main wavelength region of light absorption substantially identical with that of the yellow ink but a lower lightness than that of the yellow ink; and driving the print head based on the input control information to create dots with the plurality of basic color inks and the dark yellow ink, thereby printing an image.
The computer reads the specific program recorded in the recording medium to actualize the respective functions, so as to create dots with at least the cyan ink, the magenta ink, the yellow ink, and the dark yellow ink. This arrangement enables an image of high picture quality to be printed.
In the printing apparatus of the present invention, the dark ink is supplied by the dark ink supply unit. Other possible applications of the present invention are accordingly ink cartridges, in which the dark is kept. The present invention is thus directed to an ink cartridge detachably attached to a printing apparatus, which prints an image with a plurality of basic color inks, wherein the plurality of basic color inks are combined with one another to express achromatic color. The ink cartridge keeps therein at least one ink to be supplied to the printing apparatus. The ink cartridge has an ink reservoir that keeps therein a dark ink, the dark ink having a main wavelength region of light absorption substantially identical with that of one basic color ink selected out of the plurality of basic color inks but a lower lightness than that of the selected basic color ink.
Attachment of this ink cartridge to the printing apparatus enables the printing apparatus to create dots with the dark ink. As described previously, this arrangement enhances the degree of freedom in specification of the dot on-off conditions and improves the picture quality of the resulting printed image.
In accordance with one preferable application of the present invention, the dark ink kept in the ink cartridge has lower lightness and saturation than those of one basic color ink selected out of the plurality of basic color inks.
In accordance with another preferable application of the present invention, the dark ink kept in the ink cartridge has a main wavelength region for most strongly absorbing a ray in a visible range, which is substantially identical with that of one basic color ink selected out of the plurality of basic color inks, and a greater integral of light absorptivity in a wavelength region of the visible range than that of the selected basic color ink.
In accordance with still another preferable application of the present invention, the dark ink kept in the ink cartridge has:
(A) a characteristic wavelength region for strongly absorbing a ray in a visible range to mainly determine the hue of the dark ink, which is substantially identical with a characteristic wavelength region of one basic color ink selected out of the plurality of basic color inks;
(B) a mean value of light absorptivity that is greater than or substantially identical with a mean value of light absorptivity of the selected basic color ink in the characteristic wavelength region of the dark ink; and
(C) a mean value of light absorptivity that is greater than a mean value of light absorptivity of the selected basic color ink in a wavelength region of visible light except the characteristic wavelength region of the dark ink.
Attachment of the ink cartridge, in which any one of these dark inks is kept, to the printing apparatus enables the printing apparatus to create dots with the dark ink. This arrangement improves the picture quality of the resulting printed image.
In accordance with one preferable application of the present invention, the ink cartridge further keeps therein one basic color ink selected out of the plurality of basic color inks. In accordance with another preferable application of the present invention, the ink cartridge further keeps therein black ink, which is achromatic and has a low lightness. In accordance with still another preferable application of the present invention, the ink cartridge further keeps therein at least one light ink, which has a hue substantially identical with that of at least one basic color ink selected out of the plurality of basic color inks but a lower density than that of the at least one basic color ink.
The arrangement of keeping any of these inks in addition to the dark ink in the same ink cartridge saves the total space required for the ink cartridges, compared with separate ink cartridges that independently keep one of these inks therein.
In accordance with another preferable application of the present invention, the ink cartridge further keeps therein one basic color ink selected out of the plurality of basic color inks and at least one light ink, which has a hue substantially identical with that of at least one basic color ink selected out of the plurality of basic color inks but a lower density than that of the at least one basic color ink. The arrangement of keeping these inks together in addition to the dark ink in the same ink cartridge further saves the total space required for the ink cartridges. These color inks including the dark ink are mainly consumed in the process of printing a color image, whereas the black ink is mainly consumed in the process of printing a black and white image, for example, a document. The arrangement keeps these color inks, which are mainly consumed to print a color image, together in the same ink cartridge, separate from the black ink. This arrangement desirably enables only the ink cartridge keeping inks mainly consumed to be replaced according to the image to be printed.
The ink cartridge of the present invention may keep therein an ink having the following characteristics as the dark ink:
(A) a characteristic wavelength region that is mostly in a wavelength range of 400 nm to 500 nm, the characteristic wavelength region strongly absorbing a ray in a visible range to mainly determine the hue of the dark yellow ink; and
(B) a mean value of absorptivity of the ray in the visible range except the characteristic wavelength region, which ranges from 10% to 60%.
The ink cartridge of the present invention may alternatively keep therein an ink having the following characteristics as the dark ink:
(A) a hue included in a specific range of 10R to 10GY on a Munsell hue circle; and
(B) a saturation of smaller than 3.5C on a Munsell chroma.
Attachment of the ink cartridge, in which any of these inks is kept, to the printing apparatus enables the printing apparatus to create dots with the dark ink. This arrangement improves the picture quality of the resulting printed image.
The present invention is directed to an ink cartridge that keeps therein yellow ink and dark yellow ink, which has a lower lightness than that of the yellow ink. The present invention is also directed to an ink cartridge that keeps therein dark yellow ink and black ink. The present invention is further directed to an ink cartridge that keeps therein yellow ink, dark yellow ink, cyan ink, light cyan ink, magenta ink, and light magenta ink.
The arrangement of keeping these inks together in the same ink cartridge saves the total space required for the ink cartridges, compared with separate ink cartridges that independently keep one of these inks therein.
In accordance with one preferable application of the ink cartridge, the capacity of the dark yellow ink may be set to be greater than the capacity of the yellow ink. When a natural image, such as a landscape or a portrait, is printed, the consumption of the dark yellow ink tends to be greater than the consumption of the yellow ink. The greater capacity of the dark yellow ink than that of the yellow ink thus enables these two inks to be used up at substantially the same time. This arrangement desirably reduces the waste of ink by a replacement of the ink cartridge, in which one ink is used up but a large quantity of the other ink still remains.
The present invention is also directed to an ink cartridge that keeps therein dark yellow ink, light cyan ink and light magenta ink. The arrangement of keeping these inks together in the same ink cartridge saves the total space required for the ink cartridges, compared with separate ink cartridges that independently keep one of these inks therein. When a natural image, such as a landscape or a portrait, is printed, these inks are often consumed more than the other inks. The arrangement of keeping the dark yellow ink the light cyan ink, and the light magenta ink in the same ink cartridge enables only this ink cartridge to be replaced according to the image to be printed.
In accordance with one preferable application of the present invention, the ink cartridge further has a storage device that stores information regarding a quantity of each ink kept therein in a readable, writable, and volatile manner.
Storing the information regarding the quantity of each ink kept in the ink cartridge ensures the printing operation based on the information with regard to the accurate remaining quantity of ink. This arrangement effectively prevents the ink from being used up in the course of printing.
The storage device included in the ink cartridge may have an ink quantity information storage area, which is accessed to be written first by the printing apparatus and in which the information regarding the quantity of each ink kept in the ink cartridge is stored.
The area written first is, for example, a head area in the storage device or any area in the storage device accessible to be written first by the printing apparatus. Storing the information regarding the quantity of each ink in this area shortens the time required for writing the information. This arrangement effectively prevents the information to be written from being destroyed by cutting off the power supply of the printing apparatus in the course of the writing operation.
When the dark ink kept in the ink cartridge is used up, an ink supplier is used to feed a supply of the dark ink to the ink cartridge, so as to continue creation of dots with the dark ink and print an image of high quality. Another application of the present invention is accordingly an ink supplier. The present invention is thus directed to an ink supplier that feeds a supply of ink to an ink cartridge, wherein the ink cartridge is detachably attached to a printing apparatus and keeps therein at least one ink used by the printing apparatus. The ink supplier includes a sealed ink reservoir that keeps an ink in a sealing manner, and an ink supply unit that feeds a supply of the sealed ink to the ink cartridge. The ink sealed in the sealed ink reservoir has the following characteristics:
(A) a characteristic wavelength region that is mostly included in a wavelength range of 400 nm to 500 nm, the characteristic wavelength region strongly absorbing a ray in a visible range to mainly determine the hue of the ink; and
(B) a mean value of absorptivity of the ray in the visible range except the characteristic wavelength region, which ranges from 10% to 60%.
The ink supplier has the sealed ink reservoir that keeps an ink in a sealing manner, and the ink supply unit that feeds a supply of the sealed ink to the ink cartridge. The ink having the above characteristics (A) and (B) is sealed in the sealed ink reservoir. The characteristic wavelength region of the ink, which mainly determines the hue of the ink, is mostly included in the wavelength range of 400 nm to 500 nm. This means that the ink roughly has the hue of yellow. The ink has the mean value of absorptivity of the ray in the visible range except the characteristic wavelength region, which ranges from 10% to 60%. This means that the ink has a low lightness. The ink having the characteristics (A) and (B) is accordingly replaceable with the dark ink. In the event that the dark ink kept in the ink cartridge is used up, supply of the ink from the ink supplier to the ink cartridge enables continuous creation of dots with the dark ink to print an image of high picture quality.
The ink sealed in the ink supplier may alternatively have the following characteristics:
(A) a hue included in a specific range of 10R to 10GY on a Munsell hue circle; and
(B) a saturation of smaller than 3.5C on a Munsell chroma.
This ink may also be used as the dark ink. A supply of this ink sealed in the ink supplier to the ink cartridge enables creation of dots with the dark ink.
The technique of the present invention may be implemented by a program code that is stored in a computer to attain the functions of the printing system, the print controller, or the printing apparatus of the present invention discussed above. The computer then executes the respective functions written in the program code. A first possible application of the present invention is thus a program code, in which a method of creating dots with a plurality of different inks so as to print an image on a printing medium is written in a computer readable manner. The method actualizes the functions of: specifying dot on-off conditions with regard to a plurality of basic color inks and a dark ink based on input image data, the plurality of basic color inks being combined with one another to express achromatic color, the dark ink having a main wavelength region of light absorption substantially identical with that of one basic color ink selected out of the plurality of basic color inks but a lower lightness than that of the selected basic color ink; and controlling creation of dots with the plurality of basic color inks and the dark ink, based on the specification of the dot-on-off conditions with regard to the plurality of basic color inks and the dark ink.
A second possible application of the present invention is a program code, in which a method of supplying control information to a printer, which creates dots with a plurality of different inks on a printing medium, in order to control the creation of dots with the plurality of different inks and thereby controlling a printing operation of the printer is written in a computer readable manner. The method actualizes the functions of: specifying dot on-off conditions with regard to a plurality of basic color inks and a dark ink based on input image data, the plurality of basic color inks being combined with one another to express achromatic color, the dark ink having a main wavelength region of light absorption substantially identical with that of one basic color ink selected out of the plurality of basic color inks but a lower lightness than that of the selected basic color ink; and outputting the specification of the dot on-off conditions with regard to the plurality of basic color inks and the dark ink to the printer as the control information, so as to control the printing operation of the printer.
A third possible application of the present invention is a program code, in which a method of receiving control information to control creation of dots with a plurality of different inks and driving a print head, which creates dots with the plurality of different inks on a printing medium, based on the control information, so as to print an image is written in a computer readable manner. The method actualizes the functions of: receiving the control information to control creation of dots with a plurality of basic color inks and a dark ink, the plurality of basic color inks being combined with one another to express achromatic color, the dark ink having a main wavelength region of light absorption substantially identical with that of one basic color ink selected out of the plurality of basic color inks but a lower lightness than that of the selected basic color ink; and driving the print head based on the input control information to create dots with the plurality of basic color inks and the dark ink, thereby printing an image.
Any of the print controllers and the printing apparatuses of the present invention discussed above may provide a plurality of dark inks and uses a most suitable dark ink or the plurality of dark inks simultaneously according to an image to be printed. The present invention may accordingly have other possible applications discussed below. A fourth possible application of the present invention is thus a print controller that supplies control information to a printer, which creates dots with a plurality of different inks, in order to control the creation of dots with the plurality of different inks. The printer creates dots with a plurality of basic color inks as well as with a plurality of dark inks, wherein the plurality of basic color inks are combined with one another to express achromatic color, and each of the dark inks has a main wavelength region of light absorption substantially identical with that of one basic color ink selected out of the plurality of basic color inks but a lower lightness than that of the selected basic color ink. The print controller includes: a dot on-off condition specification unit that specifies dot on-off conditions with regard to the plurality of basic color inks and the plurality of dark inks, based on input image data; and a control information output unit that outputs the specification of the dot on-off conditions with regard to the plurality of basic color inks and the plurality of dark inks to the printer as the control information.
A fifth possible application of the present invention is a printing apparatus that has a print head to create dots with a plurality of different inks on a printing medium, receives control information to control the creation of dots with the plurality of different inks, and actually creates dots with the plurality of different inks, based on the input control information, so as to print an image. The printing apparatus includes: a basic color ink supply unit that supplies a plurality of basic color inks to the print head, wherein the plurality of basic color inks are combined with one another to express achromatic color; a dark ink supply unit that supplies a plurality of dark inks to the print head, wherein each of the dark inks has a main wavelength region of light absorption substantially identical with that of one basic color ink selected out of the plurality of basic color inks but a lower lightness than that of the selected basic color ink; a control information input unit that receives the control information with regard to dots of the plurality of basic color inks and the plurality of dark inks; and a dot formation unit that drives the print head based on the input control information, so as to create dots with the plurality of basic color inks and the plurality of dark inks.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiment with the accompanying drawings.